Invasion Plans

All creatures block each combat if able.
The attacking player chooses how each creature blocks each combat.

Ib Halfheart, Goblin Tactician

Whenever another Goblin you control becomes blocked, sacrifice it. If you do, it deals 4 damage to each creature blocking it.
Sacrifice two Mountains: Create two 1/1 red Goblin creature tokens.

Repercussion

Whenever a creature is dealt damage, Repercussion deals that much damage to that creature's controller.

Krenko, Mob Boss

{T}: Create X 1/1 red Goblin creature tokens, where X is the number of Goblins you control.